The objectives of this research proposal are to develop synthetic methods for the preparation of the quinoxaline antibiotics, a group of bicyclic depsipeptide antibiotics. Monocyclic depsipeptides will be prepared as models for preparation of the natural antibiotics. A key depsitripeptide intermediate will be condensed with appropriate cysteine derivatives to prepare the quinoxaline antibiotic triostin A. Approaches will be investigated, using alpha-acylaminoacrylic acids, to prepare alpha-mercaptocysteine derivatives and to effect conversion thereof to the dithiane amino acid moiety present in echinomycin. Resolution and stereochemical studies on the dithiane amino acids will be carried out. Structural studies will involve use of analytical, chromatographic, and spectral methods.